Orbital-engineered layered MnO₂ cathode enabled by Ca²⁺ interlayer coupling in rechargeable calcium battery

Developing multivalent-ion storage systems demands cathode materials that combine high structural adaptability with favorable orbital interactions to host sluggish, highly charged carriers such as Ca²⁺. Herein, a multi-synergistic interlayer engineering strategy is proposed via Ca²⁺ interlayer coordination. The pre-coordination of Ca²⁺ ions establishes Mn–O–Ca bridges that not only expand the interlayer distance but also reshape the local orbital field of Mn, thereby stabilizing the high-valence Mn states and suppressing Jahn-Teller distortion. Defect-induced orbital reconfiguration simultaneously enhances electronic delocalization and interlayer polarity by creating localized charge imbalances at oxygen vacancies. As a result, efficient charge transfer and Ca²⁺ diffusion are promoted, and more surface-active sites are exposed. Electrochemical evaluations reveal that Ca-MnO₂ exhibits significantly improved reversible capacity (∼100 mA h g⁻¹ at 0.1 A g⁻¹) and long-term cycling stability (1200 cycles at 1 A g⁻¹), outperforming pristine δ-MnO₂. Kinetic analysis through CV, GITT, and EIS demonstrates enhanced Ca²⁺ diffusion coefficients and reduced polarization in the pre-intercalated material. These results demonstrate an orbital-coupled interlayer engineering route toward high-performance Mn-based hosts for next-generation multivalent batteries.